Anyone enjoying movement in the garden needs to plant at least one butterfly bush (Buddleja davidii) to attract fluttering butterflies and hard-working bees. Grow butterfly bushes in moist, well-draining soil in full sunlight for best habit and copious mid- and late summer blooming. These semi-woody shrubs produce flowers on the current growing season's branches, so pruning is always a good maintenance practice.
As the butterfly bush grows in early summer, long stems emanate from the plant base. To ensure more branches develop on the primary stems, tip prune the longest stems. Removal of the tip encourages dormant buds lower on the stem to form shoots, creating a bushier look. Don't overdo tip pruning--too much causes stems to be uncharacteristically short by the time flowering starts in mid- or late summer. Tip pruning too close to midsummer also removes the immature flower clusters developing on stem tips. Consider conducting occasional, long-stem pruning to reduce the length of flowering branches that have simply gotten too long or leggy by late summer. These long, errant stems may encroach upon other garden plants or break in a heavy rain. Inadequate sunlight also leads to longer, weaker stems and branches.
After the first pointed flower cluster wanes on the tips of the shrub's stems, consider pruning it off at its base. Removal of the old flowers, called deadheading, prevents seed formation and thus encourages plants to focus energies on developing more flowers. Dormant buds at the base of leaves and at the deadheading cut will sprout and likely produce another flower cluster in a few weeks. Continual deadheading may result in flowering well into autumn.
Regardless of its size, degree of winter leaf drop or where you garden, butterfly bush should be severely pruned back to 6 to 18 inches each early spring before new growth starts. This rejuvenation pruning not only removes the thicket of old branches, it forces out fresh, new growth that is vigorous and will bloom later in summer. The shrub overall attains a more pleasant, full habit and lush, attractive foliage. This also avoids landscapes where non-pruned butterfly bushes grow large and gangly, which may warrant much more tip-pruning attention.